Bolt looseness detection system and method based on scanning laser and fixed sensor network

Abstract

The invention discloses a bolt looseness detection system and method based on scanning laser and a fixed sensor network, and belongs to the technical field of nondestructive testing. The method comprises the following steps: sequentially scanning the surface of a structure through pulse laser controlled by a galvanometer, and exciting ultrasonic waves based on a thermoelastic effect; the ultrasonic signals are synchronously collected through a piezoelectric sensor network which is fixedly arranged on the structure in a detachable mode; comparing and analyzing the acquired signal with a pre-stored reference signal, and diagnosing the pre-tightening force state of the bolt according to an analysis result; the system correspondingly comprises a pulse laser generation unit, a laser scanning control unit, a synchronous data acquisition unit and a signal processing and diagnosis unit, according to the invention, rapid, non-contact and regionalized synchronous detection of a large batch of bolts on large-scale structures such as airplanes is realized, and the detection efficiency and engineering practicability are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of non-destructive testing technology, specifically relating to a bolt loosening detection method based on scanning laser and fixed sensor network. It is particularly suitable for rapid, non-contact quantitative detection and health monitoring of the preload state of a large number of critical bolt connections in high-end equipment such as aviation and aerospace. Background Technology

[0002] In the manufacturing and service of high-end equipment such as aviation and aerospace equipment, the integrity and sealing of structural connections are crucial for ensuring safety and functionality. Tens of thousands of critical bolt connections form the first line of defense against structural failure, media leakage, and maintaining chamber pressure. Under extreme aerodynamic loads, thermal cycling, and vibration environments, even a slight decrease in the preload at these connections can trigger a chain reaction of failures, leading to catastrophic consequences. Therefore, accurate and reliable detection and monitoring of bolt preload is of paramount importance.

[0003] Currently, the commonly used methods for testing bolt preload in the industry mainly include the following, but each of these methods has its own significant limitations.

[0004] Ultrasonic testing based on the acoustoelastic effect is currently a relatively mainstream and widely used measurement method. Its principle is to infer the preload state by measuring the propagation time or velocity change of ultrasonic waves in the bolt. However, most existing ultrasonic technologies employ point-to-point contact measurement, requiring the ultrasonic probe to be individually attached to the surface of each bolt using a coupling agent for excitation and reception. This "point-to-point" operation mode faces serious efficiency bottlenecks in practical engineering. Furthermore, when the effective force-bearing length of the bolt varies due to differences in the thickness of the clamping components, different bolt specifications usually require individual calibration, a cumbersome and inflexible process. While existing technologies (such as the method disclosed in publication number CN121185495A) attempt to optimize the calibration process, their fundamental contact-based, point-to-point detection mode remains unchanged, making them unsuitable for the engineering requirements of rapid and uniform scanning of large batches of bolts of various specifications on large structures such as aircraft.

[0005] Torque control, as the most traditional control method in the assembly stage, works by indirectly ensuring preload by controlling the tightening torque. However, the coefficient of friction between bolts and connecting parts fluctuates greatly in actual assembly, resulting in a large dispersion of the final preload, making it difficult to meet high reliability requirements in terms of control accuracy. Furthermore, this method is completely unsuitable for in-service inspection and monitoring after assembly.

[0006] While the resistance strain gauge method can achieve high measurement accuracy, the operation process is cumbersome, requiring surface treatment of the bolts and installation of strain gauges, making it a destructive or semi-destructive method. This single-point measurement method is extremely time-consuming, resulting in low inspection efficiency and severely limited practicality when dealing with tens of thousands of bolts on an engineering site.

[0007] Other methods, such as optical measurement and X-ray detection, are either limited by specific measurement scenarios and high costs, or pose radiation safety risks, making it difficult to achieve rapid and universal on-site assessment of in-service equipment.

[0008] In summary, existing technologies have significant shortcomings in terms of efficiency, universality, and on-site operability. Particularly when dealing with the widespread and numerous critical bolt connections on large equipment such as aircraft, there is currently a lack of a detection method capable of non-contact, large-area rapid scanning and high-precision quantitative assessment. Therefore, developing an innovative detection scheme to shift from "point-by-point manual verification" to "regional intelligent diagnosis," thereby significantly improving detection efficiency and reliability, has become a core technical problem urgently needing to be solved in this field. Summary of the Invention

[0009] In view of this, the purpose of this invention is to provide a bolt loosening detection system and method based on scanning laser and fixed sensor network, so as to solve the technical problem of efficient, non-contact, quantitative detection and health monitoring of critical bolt connections that are widely distributed and numerous on large equipment such as aircraft, and realize the transformation from "point-by-point manual verification" to "regional intelligent diagnosis".

[0010] A bolt loosening detection system, comprising: A pulsed laser generating unit is used to generate pulsed lasers that meet the requirements. A laser scanning control unit is used to control the pulsed laser beam to scan the bolts at each detection point in sequence along the predetermined path, so that the bolts are excited with ultrasonic waves under the thermoelastic effect. A piezoelectric sensor network, comprising multiple piezoelectric sensors, is connected to the back of the structure under test to receive ultrasonic signals generated by bolts and convert them into electrical signals. The synchronous data acquisition unit includes a multi-channel data acquisition card, whose channels are respectively connected to each pressure sensor in the piezoelectric sensor network to receive the electrical signals of each pressure sensor as diagnostic signals; wherein, the acquisition of electrical signals of each pressure sensor begins simultaneously with the pulse laser generating unit emitting pulse laser. The signal processing and diagnostic unit processes the multi-channel signal data uploaded by the synchronous data acquisition unit, performs comparative analysis, and diagnoses the bolt preload state.

[0011] Preferably, the signal processing and diagnostic unit compares and analyzes each acquired diagnostic signal with a pre-stored reference signal. Specifically, it extracts at least one feature of the current signal and compares and calculates it with the feature corresponding to the reference signal, thereby diagnosing the bolt preload state. The feature includes the transit time of the ultrasonic wave from the excitation point to the pressure sensor, and / or the energy value of the signal within a set time window.

[0012] Preferably, when the transit time of the diagnostic signal is delayed by more than a first threshold relative to the transit time of the reference signal, and / or the energy value of the diagnostic signal is attenuated by more than a second threshold relative to the energy value of the reference signal, it is determined that the preload of the corresponding bolt is insufficient or that it is loose.

[0013] Preferably, the reference signal is established by performing a full-area scan and storing all diagnostic signals after the component board under test is first assembled and all bolt preload is confirmed to be within acceptable limits.

[0014] Preferably, the pulsed laser wavelength generated by the pulsed laser generating unit is located in the band where the absorption rate of the material under test is high, and the pulse width is on the order of nanoseconds to microseconds.

[0015] Preferably, the scanning path of the laser scanning control unit is a programmed path pre-set according to the distribution position of the bolts on the structure being measured.

[0016] Preferably, the piezoelectric sensor is detachably mounted to the surface of the structure under test by means of a clamp, magnetic adsorption, or peelable adhesive.

[0017] Furthermore, it also includes a display unit for visually displaying the scanning path, pressure sensor position, and status diagnostic results of each bolt.

[0018] A detection method for the above-mentioned detection system includes: The laser scanning control unit uses a galvanometer to control a pulsed laser to scan the bolts at multiple detection points on the surface of the structure under test in a predetermined path, and ultrasonic waves are sequentially excited at each detection point based on the thermoelastic effect. During each laser excitation, the ultrasonic signals received by each sensor are synchronously acquired as diagnostic signals; in particular, the electrical signals of each pressure sensor are acquired at the same time as the pulsed laser generating unit emits a pulsed laser. The signal processing and diagnostic unit processes the multi-channel signal data uploaded by the synchronous data acquisition unit, performs comparative analysis, and diagnoses the bolt preload state.

[0019] The present invention has the following beneficial effects: The detection efficiency is significantly improved. By using a galvanometer to control the laser, the rapid switching of points can be achieved in milliseconds, replacing the traditional point-to-point contact coupling operation. This allows for large-area scanning of hundreds of bolt connection points in minutes, greatly improving detection efficiency.

[0020] Achieve truly non-contact testing. The excitation end uses a pulsed laser, requiring no coupling agent or the installation or attachment of any devices to the bolt being tested, thus enabling completely non-contact measurement, especially suitable for applications where surfaces cannot be touched or in harsh environments.

[0021] Adaptable to complex structures and large-volume inspection. The sensor network can be deployed in a detachable manner (such as magnetic adsorption) and can be used in conjunction with laser scanning to complete the inspection of the entire area. It has strong system integration and is particularly suitable for the rapid inspection of a large number of bolts on large and complex structures such as aircraft skin and spacecraft panels.

[0022] The diagnostic mechanism is profound and the results are reliable. This invention is based on the physical mechanism of "bolt preload - contact interface stiffness - ultrasonic coupling efficiency" for diagnosis. By analyzing the attenuation of ultrasonic signal energy, the interface state is directly assessed, with clear physical meaning, avoiding misjudgments that may be caused by a single parameter, making the diagnostic conclusions more scientific and reliable, and facilitating rapid and accurate decision-making on the engineering site. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the bolt loosening detection system of the present invention, which uses a scanning laser and a fixed sensor network. Among them, 1-pulse laser, 2-XY galvanometer, 3-test component board, 4-bolt, 5-ultrasonic sensor, 6-data acquisition module, and 7-data processing module. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] The core principle of this invention lies in the fact that the preload of the bolt directly determines the stiffness and tightness of the contact interface between it and the connecting parts. When the bolt is normally tightened, the interface is tightly bonded, and ultrasonic waves can propagate efficiently through the interface, resulting in strong and clear signal energy received by the sensor. However, when the bolt loosens, the stiffness of the contact interface decreases, creating micro-gaps or poor contact, leading to severe scattering and energy attenuation of ultrasonic waves at the interface, and a significant reduction in the energy of the received signal. Therefore, by accurately detecting and comparing the energy (or amplitude) characteristics of the ultrasonic signal, the attenuation or loosening of the bolt preload can be directly and sensitively diagnosed from a physical mechanism perspective.

[0026] This invention combines non-contact, programmable, rapid scanning laser ultrasonic excitation technology with fixed, networked, synchronous acquisition piezoelectric sensing technology to construct a novel regional synchronous detection mode.

[0027] In a first aspect, the present invention provides a rapid detection system for bolt preload condition in large-area structures, comprising: A pulsed laser generating unit is used to generate pulsed lasers that meet the requirements. The laser scanning control unit includes a galvanometer assembly and its controller, used to control the pulsed laser beam to scan the bolts at each detection point in sequence along the predetermined path, so that the bolts are excited with ultrasonic waves under the thermoelastic effect; A piezoelectric sensor network, comprising multiple piezoelectric sensors, is connected to the back of the board of the component under test to receive ultrasonic signals generated by the bolts and convert them into electrical signals. The synchronous data acquisition unit includes a multi-channel data acquisition card, with each channel connected to a pressure sensor in the piezoelectric sensor network to receive electrical signals from each pressure sensor. Simultaneously with the pulsed laser generation unit emitting a pulsed laser, the electrical signals from each pressure sensor are acquired, ensuring synchronization between the pressure sensor signals and the pulsed laser, thus guaranteeing the consistency of the signal acquisition timing.

[0028] The signal processing and diagnostic unit is used to store and process the multi-channel signal data uploaded by the synchronous data acquisition unit, and to perform comparative analysis to diagnose the urgency of the bolt preload state.

[0029] Secondly, this invention provides a rapid detection method for bolt preload state in large-area structures, comprising the following steps: The pulsed laser is controlled to scan multiple detection points on the surface of the structure under test in sequence along a pre-planned path, and ultrasonic waves are excited at each detection point based on the thermoelastic effect.

[0030] By using a piezoelectric sensor network that is detachably fixed to the structure under test, the ultrasonic signals received by each sensor are synchronously acquired at each laser excitation moment, forming multi-channel signal data.

[0031] The multi-channel signals collected during each excitation are compared and analyzed with pre-stored reference signals. The reference signals are signals pre-collected and stored under the same detection point and sensor layout, with each bolt under normal preload.

[0032] Based on the results of the comparative analysis, the preload status of the bolts associated with each test point is diagnosed, such as determining whether the preload is sufficient or whether it has become loose.

[0033] Example: Please see Figure 1 The diagram illustrates a structural schematic of a rapid bolt preload state detection system according to an embodiment of the present invention. The system mainly includes a laser excitation and scanning module, an ultrasonic sensing and acquisition module, and a central control and processing module.

[0034] The laser excitation and scanning module includes a pulsed laser 1 and an XY galvanometer 2. The pulsed laser 1 generates a high-energy pulsed laser with a wavelength selectable from the band of high absorption of the material under test, such as aluminum alloy, for example, the common 1064nm near-infrared light. The pulse width is on the order of nanoseconds to microseconds to ensure effective excitation of ultrasonic waves through thermoelasticity while avoiding ablation damage to the component surface. The XY galvanometer 2 is driven by a high-precision scanning lens and an independent galvanometer controller. It receives instructions from the control system to quickly and accurately deflect and focus the pulsed laser beam onto a preset scanning position on the surface of the component plate 3 under test.

[0035] During operation, the pulsed laser is irradiated onto the surface of the bolt 4 after being controlled by the galvanometer 2. The surface of the bolt 4 absorbs the laser energy and generates instantaneous thermal expansion, which excites ultrasonic waves in the bolt based on the thermoelastic effect. The excited ultrasonic waves are first transmitted to the test component plate 3 connected to it and propagate within the plate. Finally, the ultrasonic waves are transmitted to the ultrasonic sensor network composed of multiple ultrasonic sensors 5 arranged on the back of the plate and converted into electrical signals by the sensor network.

[0036] The ultrasonic sensing and acquisition module includes a sensor network consisting of multiple ultrasonic sensors 5 arranged on the test component plate 3, and a data acquisition module 6. The ultrasonic sensors 5 are composed of multiple broadband piezoelectric sensors, for example, four, with a center frequency selectable to be 1MHz. These sensors are detachably fixed to specific locations on the back of the structure under test, for example by magnetic adsorption bases or peelable coupling agents. In this embodiment, four sensors 5 are arranged at the four corners of the back of a plate-shaped test component plate 3 with multiple bolts 4, to receive ultrasonic signals from different directions. The outputs of all sensors 5 are connected to the input channels of the multi-channel data acquisition module 6 via coaxial cables.

[0037] The core of the central control and processing module is the data processing module 7, typically implemented by an industrial computer or embedded system. The data processing module 7 is connected via a control bus to the controllers of the pulsed laser 1, the XY galvanometer 2, and the data acquisition module 6. The system's workflow is coordinated and controlled by dedicated software running on the data processing module 7: first, it plans the scanning path and drives the galvanometer 2 to position itself; then, it triggers the pulsed laser 1 to emit laser light; simultaneously, it sends a hardware synchronization trigger signal to the data acquisition module 6 to ensure strict synchronization between the acquisition of the ultrasonic signal and laser excitation. The data acquisition module 6 uploads the acquired multi-channel waveform data to the data processing module 7 in real time for processing, analysis, and storage.

[0038] The following example demonstrates the specific implementation process of using this system for testing bolt connections on an aircraft skin panel.

[0039] The first step is system calibration and benchmark database establishment. This step is performed on a benchmark component where all bolt preloads are known to meet technical requirements. The operator first fixes four or more ultrasonic sensors 5 to the back of the benchmark component in a predetermined layout. Then, the digital model of the component or bolt coordinates are imported into the software of the data processing module 7. The software automatically generates a laser scanning path sequence covering the head or surrounding designated area of ​​all bolts 4 to be tested. After setting up, the "benchmark learning" mode is activated. The system controls the pulsed laser 1 and XY galvanometer 2 to automatically run along the path. At each scanning point, a laser pulse is triggered, and simultaneously, the data processing module 7 sends a synchronous trigger signal to the data acquisition module 6, completely acquiring and recording the ultrasonic waveforms of all sensor channels. Finally, the system correlates the multi-channel waveform data corresponding to all scanning points with their spatial coordinates to form a complete "benchmark signal database." This database characterizes the acoustic features of each bolt-sensor path in a healthy state.

[0040] The second step is in-service inspection and data acquisition. When it is necessary to inspect in-service components, multiple ultrasonic sensors 5 are first fixed on their surface in the same layout as the calibration time. The same scanning path and the established "reference signal database" are loaded into the software of the data processing module 7. After the inspection program is started, the system automatically executes the scanning cycle. For each target scanning point, the data processing module 7 first drives the XY galvanometer 2 to position the laser beam at that point, and then triggers the pulsed laser 1 to emit a pulse. At the same moment of laser excitation, the data processing module 7 sends a hardware synchronization trigger signal to the data acquisition module 6, and the data acquisition module 6 then synchronously samples all sensor channels and uploads the multi-channel waveform data frame corresponding to this excitation to the data processing module 7. This process is performed sequentially until the scanning of all bolt points is completed.

[0041] The third step is signal processing and feature extraction. The data processing module 7 processes the massive amount of data collected. For data collected from any scanning point, which corresponds to a specific bolt 4, the system first retrieves the corresponding reference waveform from the "reference signal database" based on its coordinates. By comparing the current waveform with the reference waveform, the system can confirm the validity of the signal. It is important to note that the preload of bolt 4 directly determines the contact interface characteristics between it and the plate 3 under test. When bolt 4 is properly tightened, a tight, high-rigidity mechanical contact is formed between the bolt head and the plate, providing an efficient coupling path for ultrasonic waves to travel from the bolt to the plate. Therefore, the ultrasonic sensor 5 can receive a strong ultrasonic signal. Conversely, when bolt 4 is loose, the contact interface pressure decreases or even micro-gaps are generated, leading to a significant decrease in interface contact stiffness. Ultrasonic waves will experience severe scattering and energy attenuation when passing through this interface, and the signal energy ultimately received by the ultrasonic sensor 5 will be significantly weakened. Therefore, the intensity (energy or amplitude) of the ultrasonic signal is a direct and sensitive characteristic quantity characterizing the contact state of the bolt-plate interface, and thus diagnosing whether the bolt preload is loose. The core processing involves extracting the ultrasonic signal characteristics characterizing the bolt's stress state, mainly including the ultrasonic transit time and signal energy. The system uses a cross-correlation algorithm to calculate the time delay between the current detected waveform and the reference waveform; this delay is the change in transit time. Simultaneously, the system calculates the root mean square value or integral of the signal within a specific time window to obtain the current signal energy value, and compares it with a reference energy to calculate the energy attenuation rate. .

[0042] The fourth step is state diagnosis and visualization output. The system sets pre-calibrated thresholds for diagnosis, such as the threshold for the change in transit time. The signal energy attenuation rate threshold is 2 microseconds. The percentage is 50%. For each inspected bolt 4, the system analyzes the data from all corresponding sensor channels. The diagnostic logic comprehensively considers two characteristics: the change in transit time. This reflects the overall change in the propagation path length of the ultrasound wave; while the signal energy attenuation rate... This directly and sensitively reflects the decrease in ultrasonic coupling efficiency at the bolt 4-plate 3 interface, providing strong evidence of contact interface loosening and reduced preload. If the transit time of any channel changes... Exceeding the threshold or signal energy attenuation rate Exceeding the threshold If the preload of bolt 4 is insufficient, it is determined that there is a risk of loosening. After the diagnosis is completed, the results are displayed intuitively in the software interface: on the component diagram, all inspected bolts 4 are marked with different colors, for example, green represents normal and red represents abnormal. At the same time, the system can generate a structured inspection report, which lists in detail the number, location and specific characteristic deviation value of the abnormal bolt 4.

[0043] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A bolt loosening detection system, characterized in that, include: A pulsed laser generating unit is used to generate pulsed lasers that meet the requirements. A laser scanning control unit is used to control the pulsed laser beam to scan the bolts at each detection point in sequence along the predetermined path, so that the bolts are excited with ultrasonic waves under the thermoelastic effect. A piezoelectric sensor network, comprising multiple piezoelectric sensors, is connected to the back of the structure under test to receive ultrasonic signals generated by bolts and convert them into electrical signals. The synchronous data acquisition unit includes a multi-channel data acquisition card, whose channels are respectively connected to each pressure sensor in the piezoelectric sensor network to receive the electrical signals of each pressure sensor as diagnostic signals; wherein, the acquisition of electrical signals of each pressure sensor begins simultaneously with the pulse laser generating unit emitting pulse laser. The signal processing and diagnostic unit processes the multi-channel signal data uploaded by the synchronous data acquisition unit, performs comparative analysis, and diagnoses the bolt preload state.

2. The bolt loosening detection system as described in claim 1, characterized in that, The signal processing and diagnostic unit compares and analyzes each acquired diagnostic signal with a pre-stored reference signal. Specifically, it extracts at least one feature of the current signal and compares and calculates it with the feature corresponding to the reference signal, thereby diagnosing the bolt preload state. The feature includes the transit time of the ultrasonic wave from the excitation point to the pressure sensor, and / or the energy value of the signal within a set time window.

3. The bolt loosening detection system as described in claim 2, characterized in that, When the transit time of the diagnostic signal is delayed by more than a first threshold relative to the transit time of the reference signal, and / or the energy value of the diagnostic signal is attenuated by more than a second threshold relative to the energy value of the reference signal, it is determined that the preload of the corresponding bolt is insufficient or that it is loose.

4. The bolt loosening detection system as described in claim 3, characterized in that, The reference signal is established by performing a full-area scan and storing all diagnostic signals after the component board under test is first assembled and all bolt preload is confirmed to be within acceptable limits.

5. The bolt loosening detection system as described in claim 3, characterized in that, The pulsed laser generating unit generates pulsed laser wavelengths in the band where the absorption rate of the material under test is high, and the pulse width is in the range of nanoseconds to microseconds.

6. The bolt loosening detection system as described in claim 3, characterized in that, The scanning path of the laser scanning control unit is a pre-programmed path based on the distribution of bolts on the structure being measured.

7. The bolt loosening detection system as described in claim 3, characterized in that, The piezoelectric sensor is detachably mounted to the surface of the structure being measured by means of a clamp, magnetic adsorption, or peelable adhesive.

8. The bolt loosening detection system as described in claim 3, characterized in that, It also includes a display unit for visually displaying the scan path, pressure sensor location, and status diagnostic results of each bolt.

9. A detection method for the detection system according to any one of claims 1 to 8, characterized in that, include: The laser scanning control unit uses a galvanometer to control a pulsed laser to scan the bolts at multiple detection points on the surface of the structure under test in a predetermined path, and ultrasonic waves are sequentially excited at each detection point based on the thermoelastic effect. During each laser excitation, the ultrasonic signals received by each sensor are synchronously acquired as diagnostic signals; in particular, the electrical signals of each pressure sensor are acquired at the same time as the pulsed laser generating unit emits a pulsed laser. The signal processing and diagnostic unit processes the multi-channel signal data uploaded by the synchronous data acquisition unit, performs comparative analysis, and diagnoses the bolt preload state.

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